Generally, in a spark-ignition internal combustion engine, in order to increase engine output torque or reduce exhaust emissions, ignition timing is controlled based on various vehicle operating conditions such as engine speed engine load, etc.
A problem with corner ignition timing control methods is that the ignition timing value in an idle state or a partial load state during a predetermined period after starting of the engine is determined near a minimum spark advance for best torque value (MBT) without considering the coolant temperature.
Accordingly, if the coolant temperature is low, its temperature increases slowly, and a relatively long period expires before the temperature of the emission gas reaches a light off temperature where an operational efficiency of a catalytic converter is maximized. Thus, a large amount of emission gas is exhausted before reaching the light off temperature.